<template>
	<ul class="list">
		<li 
			v-for="item of letters" 
			:key="item"
			:ref="item"
			@click="handleLetterClick"
			@touchstart="handleTounchStart"
			@touchmove="handleTouchMove"
			@touchend="handleTouchEnd"
		>
		{{item}}
		</li>
	</ul>
</template>
<script>
export default{
	name:'CityAlphabet',
	props:{
		cities:Object
	},
	computed: {
		letters () {
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus :false,
			startY: 0,
			timer: null
		}
	},
	update () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods:{
		handleLetterClick(e){
			this.$emit('change',e.target.innerText)
		},
		handleTounchStart () {
			this.touchStatus = true
		},
		handleTouchMove (e) {
			if (this.touchStatus) {
				if(this.timer) {
					clearTimeout(this.timer)
				}
				this.timer = setTimeout( () => {
					const touchY = e.touches[0].clientY - 79
					const index = Math.floor((touchY - this.startY) / 20)
					if(index >= 0 && index < this.letters.length ) {
						this.$emit('change',this.letters[index])
					}
				},16)
				
			}
		},
		handleTouchEnd () {
			this.touchStatus =  false
		}
	}
}
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl'
	.list
		display:flex
		position:absolute
		top:1.58rem
		right:0
		bottom:0
		flex-direction:column
		justify-content:center
		text-align:center
		width:.4rem
		li
			line-height:.4rem
			color:$bgcolor
</style>